Weichai Transactions (Details) - Share Purchase Agreement, Weichai Transaction - USD ($)	1 Months Ended		12 Months Ended
	Nov. 30, 2017	Mar. 31, 2017	Dec. 31, 2019
Subsidiary, Sale of Stock [Line Items]
Consideration received on transaction		$ 60,000,000
Common Stock
Subsidiary, Sale of Stock [Line Items]
Number of shares issued in transaction (in shares)		2,728,752	4,050,000
Redeemable Convertible Series B Preferred Stock
Subsidiary, Sale of Stock [Line Items]
Number of shares issued in transaction (in shares)		2,385,624
Issuance of redeemable convertible Series B Preferred Stock, net of fees (in shares)	4,771,248